We compared the acute effects of bilateral arteriovenous fistulas to those of hydralazine infusion on hemodynamics and pulmonary gas exchange in dogs with pulmonary edema induced by administration of oleic acid. Oleic acid significantly (p < .01) increased intrapulmonary shunt (Q̇sp/Q̇t) and pulmonary and systemic vascular resistance, and reduced cardiac output. Once the lesion stabilized, both opening the fistula and infusing hydralazine produced a similar and significant (p < .01) increase in cardiac output, and a significant (p < .05) decrease in resistance. Mixed venous oxygen tension (Pvō2) closely followed the changes in cardiac output; however, Pao2 did not change. Q̇sp/Q̇t significantly (p < .01) increased with the fistulas open and with hydralazine infusion. Closure of the fistulas or bleeding the animal at the end of the experiment reversed the changes in cardiac output and Q̇sp/Q̇t. The comparable increases in cardiac output and Q̇sp/Q̇t produced by opening the fistulas or infusing hydralazine may be related to levels of Pv̄o2. The hydralazine-associated Pv̄o2 increased indicates that this drug increased oxygen transport to the tissues even as Q̇sp/Q̇t became larger.